1. Field of the Invention
This invention relates to power transmission belts and, more particularly, to a power transmission belt that may have a plurality of ribs extending lengthwise of a body on the belt. The invention is further directed to a method of forming such a power transmission belt.
2. Background Art
V-ribbed power transmission belts are used in many different environments. Typically, a V-ribbed belt has a compression section, in which a plurality of ribs are formed that extend in a lengthwise direction with respect to the belt body. A cushion rubber layer is applied to the compression section and has at least one load carrying member/cord embedded therein. To the cushion rubber layer, a layer, typically of canvas, is applied so as to be exposed on the belt body. The canvas layer increases the lengthwise crack resistance of the belt body. Typically, the canvas layer is made by rubber coating a flat fabric having woven warp and weft components.
In one application, a V-ribbed belt is trained around a driving pulley and a driven pulley with an inside of the belt engaged to drive/be driven by associated pulleys. The outside of the belt is engaged by an idler pulley. The interaction of the idler pulley and belt tends to generate unwanted noise. This noise generation may occur as the idler pulley contacts a seam where the ends of the canvas layer are joined. Noise generation may occur at other than this seam location. One of the causes for this latter type of noise generation results from the surface configuration for the canvas layer that contacts the idler pulley.
During formation of a bias canvas or cylindrical canvas, and/or during fitting of a cylindrical canvas onto a belt forming structure, the canvas mechanically deforms, as a result of which the crossing angles of warp and weft, and the size of the surrounding meshes, may vary. This irregularity results in local concentrations of the warp and weft components. As the idler pulley engages the areas having different surface characteristics, noise may be generated.
One way to avoid the above condition is to eliminate the canvas layer, whereby a rubber component becomes directly exposed to engage the idler pulley. However, with this construction adhesive wear is likely to occur, which may generate another type of noise, such as a slip sound in operation.
To avoid this latter condition, short fibers may be mixed into the exposed rubber layer that engages the idler pulley. Such a construction is shown in U.S. Patent Application Publication No. US2005/0003918 (Hiyashi). Hiyashi teaches to control the orientation of the short fibers in the exposed rubber layer so as to avoid noise generation.
With Hiyashi's construction, there is a danger that the belt body may be prone to splitting lengthwise in trough regions between adjacent ribs. Alternatively, cracks may be generated in the belt width direction at an end portion of the belt body from at this surface. This type of belt is particularly prone to a lengthwise split or cracking in the event that ethylene/α-olefin is used as the elastomer to define the belt body. In the event a peroxide cross link material is used, the likelihood of tearing is even further increased.
To avoid lengthwise splitting in the trough region between adjacent teeth, the lengths of the short fibers may be aligned to extend laterally between the sides of the belt body. Alternatively, to reduce the likelihood of crack generation, the short fibers may be oriented so that their lengths align generally with the length of the belt body. Generally, designers using the short fibers for purposes of reinforcement have been required to focus on either avoiding lengthwise cracking or cracking at an end portion. It is difficult, using the construction as in Hiyashi, to effectively address both the problems of lengthwise splitting and cracking of an end portion of the belt body.